Cape Town - It’s alien versus alien in Zeekoevlei, Cape Town, these days – and although they’re both from South America, one of them is the good guy everyone is rooting for, while the other is the bad guy who will hopefully be obliterated.
And if that sounds a bit extreme, it’s okay, because the bad guy is the water hyacinth, one of the fastest-growing plants known that now ranks among the world’s worst alien invasives and causes damage calculated in billions of dollars.
The seven attractive but deadly species that constitute the genus Eichhornia have been spread through the exotic plant trade into rivers and water bodies in North America, Asia, Australia, Africa (introduced in South Africa in 1910) and New Zealand.
Cape Town is not exempt, and the free-floating plant is a major problem, including in Zeekoevlei. Recently, the city released hopper insects from Argentina here in a bid to help control this invasive, as part of its celebration of the recent National Weedbuster Day.
This is the first time this insect has been released in South Africa, and it follows extensive research by entomologists at Rhodes University in Grahamstown. They work on the effectiveness of biological control, or biocontrol, agents – insects, mites and pathogens – specifically for water hyacinth, which is rated as South Africa’s worst aquatic weed.
The chosen release site at Zeekoevlei is clogged with water hyacinth and is an ideal spot for releasing natural enemies because they multiply and remain in the area, the city says.
Also, the site is that part of the Zeekoevlei wetland that is largely inaccessible to the Kader Asmal River Warden alien-clearing teams because it’s the home of hippos that pose a threat to these workers.
Although a suite of other biological control agents has been released into the city’s waterways to help fight the water hyacinth invasion, and mechanical and manual clearing is also done, the plant remains a significant problem.
“This is largely as a result of our sunny climate and the many nutrient-enriched rivers, dams and waterways which provide a constant supply of food for its ever-expanding growth,” the city says.
Scientists accept that water hyacinth will not be eradicated from the city’s waterways due to its long-lasting seed bank. But by combining all options the city hopes for an acceptable level of control, and that the newest weapon will go a long way in helping to achieve this. - Cape Argus